CSHARP-5834: Fix racy backpressure-network-* tests

[sanych-sun]

No description provided.

[Copilot]

Pull request overview

This PR addresses race conditions in the backpressure-network-* test suite by splitting topology-agnostic tests into topology-specific variants and adding support for replica set server type matching in the unified test event matcher.

Changes:

• Added support for RSPrimary and RSSecondary server types in the unified event matcher
• Split backpressure tests into separate single and replicaset topology-specific test files
• Updated test files to wait for specific server description states (Standalone or RSPrimary) instead of generic events

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
UnifiedEventMatcher.cs	Added RSPrimary and RSSecondary server type mappings to support replica set server type filtering in tests
backpressure-network-timeout-fail-single.yml	Restricted test to single topology and added Standalone server type assertion
backpressure-network-timeout-fail-single.json	JSON equivalent of the single topology test restrictions
backpressure-network-timeout-fail-replicaset.yml	New replicaset-specific test variant with RSPrimary server type assertion
backpressure-network-timeout-fail-replicaset.json	JSON equivalent of the replicaset topology test
backpressure-network-error-fail-single.yml	Restricted test to single topology and changed event monitoring from heartbeat to server description with Standalone type
backpressure-network-error-fail-single.json	JSON equivalent of the network error single topology test
backpressure-network-error-fail-replicaset.yml	New replicaset-specific network error test with RSPrimary server type assertion
backpressure-network-error-fail-replicaset.json	JSON equivalent of the replicaset network error test

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